Obviously number 6 is incorrect.
The sentence contains a double negative. So you are actually saying 'I know something about you'.
It is correct to say' I don't know anything about you'.

This is an answer from England. American usage is slightly different, especially in the area of talk to/talk with. I believe both are correct in American English, but talk with is a more modern usage, and is so far not correct English English. "Speak with" tends (in English English) to mean that I have a topic to discuss with you, for example "I need to speak with you about this before we make a decision" while "speak to" does not imply a discussion, just a wish to have a chat, as in "I'm busy today, but I want to speak to you this week."

The sentence "I don't know nothing about you" is wrong in any jurisdiction (American or English English). In some languages a double negative makes the negative stronger, but in English double negatives are wrong. The correct English sentences are "I know nothing about you" and "I don't know anything about you". Again, American English is slightly different from English English, but I'm not able to be clearer about this.

Finally, "I am being very honest to you so far" sounds to me like English spoken by a Spaniard. In American or English English, the phrase is "honest with", not "honest to".